211 research outputs found
Phase Diagrams for Sonoluminescing Bubbles
Sound driven gas bubbles in water can emit light pulses. This phenomenon is
called sonoluminescence (SL). Two different phases of single bubble SL have
been proposed: diffusively stable and diffusively unstable SL. We present phase
diagrams in the gas concentration vs forcing pressure state space and also in
the ambient radius vs gas concentration and vs forcing pressure state spaces.
These phase diagrams are based on the thresholds for energy focusing in the
bubble and two kinds of instabilities, namely (i) shape instabilities and (ii)
diffusive instabilities. Stable SL only occurs in a tiny parameter window of
large forcing pressure amplitude atm and low gas
concentration of less than of the saturation. The upper concentration
threshold becomes smaller with increasing forcing. Our results quantitatively
agree with experimental results of Putterman's UCLA group on argon, but not on
air. However, air bubbles and other gas mixtures can also successfully be
treated in this approach if in addition (iii) chemical instabilities are
considered. -- All statements are based on the Rayleigh-Plesset ODE
approximation of the bubble dynamics, extended in an adiabatic approximation to
include mass diffusion effects. This approximation is the only way to explore
considerable portions of parameter space, as solving the full PDEs is
numerically too expensive. Therefore, we checked the adiabatic approximation by
comparison with the full numerical solution of the advection diffusion PDE and
find good agreement.Comment: Phys. Fluids, in press; latex; 46 pages, 16 eps-figures, small
figures tarred and gzipped and uuencoded; large ones replaced by dummies;
full version can by obtained from: http://staff-www.uni-marburg.de/~lohse
Fusion yield: Guderley model and Tsallis statistics
The reaction rate probability integral is extended from Maxwell-Boltzmann
approach to a more general approach by using the pathway model introduced by
Mathai [Mathai A.M.:2005, A pathway to matrix-variate gamma and normal
densities, Linear Algebra and Its Applications}, 396, 317-328]. The extended
thermonuclear reaction rate is obtained in closed form via a Meijer's
G-function and the so obtained G-function is represented as a solution of a
homogeneous linear differential equation. A physical model for the
hydrodynamical process in a fusion plasma compressed and laser-driven spherical
shock wave is used for evaluating the fusion energy integral by integrating the
extended thermonuclear reaction rate integral over the temperature. The result
obtained is compared with the standard fusion yield obtained by Haubold and
John in 1981.[Haubold, H.J. and John, R.W.:1981, Analytical representation of
the thermonuclear reaction rate and fusion energy production in a spherical
plasma shock wave, Plasma Physics, 23, 399-411]. An interpretation for the
pathway parameter is also given.Comment: 17 pages, LaTe
Thermal performance of the European flat oyster, Ostrea edulis (Linnaeus, 1758)—explaining ecological findings under climate change
Detonation Initiation via Imploding Shock Waves
An imploding annular shock wave driven by a jet of air was used to initiate detonations
inside a 76 mm diameter tube. The tube was filled with a test gas composed of either
stoichiometric ethylene-oxygen or propane-oxygen diluted with nitrogen. The strength of
the imploding shock wave and the sensitivity of the test gas were varied in an effort to
find the minimum shock strength required for detonation of each test mixture. The results
show that the minimum required shock strength increases with mixture sensitivity and
suggest that impractically large shock driver pressures are required to initiate detonations
in ethylene-air or propane-air mixtures when using this technique
Multidimensional Conservation Laws: Overview, Problems, and Perspective
Some of recent important developments are overviewed, several longstanding
open problems are discussed, and a perspective is presented for the
mathematical theory of multidimensional conservation laws. Some basic features
and phenomena of multidimensional hyperbolic conservation laws are revealed,
and some samples of multidimensional systems/models and related important
problems are presented and analyzed with emphasis on the prototypes that have
been solved or may be expected to be solved rigorously at least for some cases.
In particular, multidimensional steady supersonic problems and transonic
problems, shock reflection-diffraction problems, and related effective
nonlinear approaches are analyzed. A theory of divergence-measure vector fields
and related analytical frameworks for the analysis of entropy solutions are
discussed.Comment: 43 pages, 3 figure
Diet-Independent Remodeling of Cellular Membranes Precedes Seasonally Changing Body Temperature in a Hibernator
Polyunsaturated fatty acids (PUFA) have a multitude of health effects. Their incorporation into membrane phospholipids (PL) is generally believed to depend directly on dietary influx. PL influence transmembrane protein activity and thus can compensate temperature effects; e.g. PL n-6 PUFA are thought to stabilize heart function at low body temperature (Tb), whereas long chain (>C18) n-3 PUFA may boost oxidative capacity. We found substantial remodeling of membranes in free-living alpine marmots which was largely independent of direct dietary supply. Organ PL n-6 PUFA and n-6 to n-3 ratios were highest at onset and end of hibernation after rapid increases during a brief transitional period prior to hibernation. In contrast, longer chain PL n-3 PUFA content was low at end of summer but maximal at end of hibernation. After termination of hibernation in spring, these changes in PL composition were rapidly reversed. Our results demonstrate selective trafficking of PUFA within the body, probably governed by a circannual endogenous rhythm, as hibernating marmots were in winter burrows isolated for seven months from food and external cues signaling the approaching spring. High concentrations of PL n-6 PUFA throughout hibernation are in line with their hypothesized function of boosting SERCA 2a activity at low Tb. Furthermore, we found increasing rate of rewarming from torpor during winter indicating increasing oxidative capacity that could be explained by the accumulation of long-chain PL n-3 PUFA. It may serve to minimize the time necessary for rewarming despite the increasing temperature range to be covered, because rewarming is a period of highest metabolic rate and hence production of reactive oxygen species. Considering the importance of PUFA for health our results may have important biomedical implications, as seasonal changes of Tb and associated remodeling of membranes are not restricted to hibernators but presumably common among endothermic organisms
Analysis of preconditioning and multigrid for Euler flows with low-subsonic regions
For subsonic flows and upwind-discretized, linearized 1-D Euler equations, the smoothing behavior of multigrid-accelerated point Gauss-Seidel relaxation is analyzed. Error decay by convection across domain boundaries is also discussed. A fix to poor convergence rates at low Mach numbers is sought in replacing the point relaxation applied to unconditioned Euler equations, by locally implicit “time”-stepping applied to preconditioned Euler equations. The locally implicit iteration step is optimized for good damping of high-frequency errors. Numerical inaccuracy at low Mach numbers is also addressed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/41714/1/10444_2005_Article_BF02123476.pd
Effects of oil and global environmental drivers on two keystone marine invertebrates
Ocean warming (OW) and acidification (OA) are key features of global change and are predicted to have negative consequences for marine species and ecosystems. At a smaller scale increasing oil and gas activities at northern high latitudes could lead to greater risk of petroleum pollution, potentially exacerbating the effects of such global stressors. However, knowledge of combined effects is limited. This study employed a scenario-based, collapsed design to investigate the impact of one local acute stressor (North Sea crude oil) and two chronic global drivers (pH for OA and temperature for OW), alone or in combination on aspects of the biology of larval stages of two key invertebrates: the northern shrimp (Pandalus borealis) and the green sea urchin (Strongylocentrotus droebachiensis). Both local and global drivers had negative effects on survival, development and growth of the larval stages. These effects were species- and stage-dependent. No statistical interactions were observed between local and global drivers and the combined effects of the two drivers were approximately equal to the sum of their separate effects. This study highlights the importance of adjusting regulation associated with oil spill prevention to maximize the resilience of marine organisms to predicted future global conditions
Novel reptilian uncoupling proteins: molecular evolution and gene expression during cold acclimation
Many animals upregulate metabolism in response to cold. Uncoupling proteins (UCPs) increase proton conductance across the mitochondrial membrane and can thereby alleviate damage from reactive oxygen species that may form as a result of metabolic upregulation. Our aim in this study was to determine whether reptiles (Crocodylus porosus) possess UCP genes. If so, we aimed to place reptilian UCP genes within a phylogenetic context and to determine whether the expression of UCP genes is increased during cold acclimation. We provide the first evidence that UCP2 and UCP3 genes are present in reptiles. Unlike in other vertebrates, UCP2 and UPC3 are expressed in liver and skeletal muscle of the crocodile, and both are upregulated in liver during cold acclimation but not in muscle. We identified two transcripts of UCP3, one of which produces a truncated protein similar to the UCP3S transcript in humans, and the resulting protein lacks the predicted nucleotide-binding regulatory domain. Our molecular phylogeny suggests that uncoupling protein 1 (UCP1) is ancestral and has been lost in archosaurs. In birds, UCP3 may have assumed a similar function as UCP1 in mammals, which has important ramifications for understanding endothermic heat production
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